Adaptive receive and omnidirectional transmit antenna array

ABSTRACT

An adaptive antenna used in a receive only mode with a separate omnidirectional transmit antenna. The arrangement is especially effective for small, handheld wireless devices. The transmit antenna maybe integrated with the receive array by utilizing a horizontally polarized transmit and vertically polarized receiver ray. In other embodiments, the transmit antenna may be physically separate and not integrated with the receive array. In either case there is separate receive and transmit signal port as an interface to radio transceiver equipment. The use of an adaptive antenna in the receive only direction has the potential to increase forward links capacity to levels equal to or greater than reverse link capacity. This allows for a significant increase in the overall number of users that may be active at the same time in a wireless system.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/386,393, filed Mar. 10, 2003, now U.S. Pat. No. 6,873,293 whichclaims the benefit of U.S. Provisional Application No. 60/363,144, filedon Mar. 8, 2002. The entire teachings of the above applications areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to wireless communication systems and inparticular to a compact, configurable antenna apparatus for use with aportable subscriber unit.

BACKGROUND OF THE INVENTION

Code Division Multiple Access (CDMA) modulation and other spreadspectrum techniques now find widespread application in wireless systemssuch as cellular mobile telephones, wireless local area networks andsimilar systems. In these systems a connection is provided between acentral hub or base station and one or more mobile or remote subscriberunits. The base station typically includes a specialized antenna forsending forward link radio signals to the mobile subscriber units andfor receiving reverse link radio signals transmitted from the mobileunits. Each mobile subscriber unit also contains its own antenna, forthe reception of the forward link signals and for transmission ofreverse link signals. A typical mobile subscriber unit may for example,be a digital cellular telephone handset or a personal digital assistanthaving an incorporated cellular modem, or other wireless data device. InCDMA systems, multiple mobile subscriber units are typicallytransmitting and receiving signals on the same carrier frequency at thesame time. Unique modulation codes distinguish the signals originatingfrom or intended to be sent to individual subscriber units.

Other wireless access techniques also use spread spectrum forcommunications between a centralized unit and one or more remote ormobile units. These include the local area network standard promulgatedby the Institute of the Electrical and Electronic Engineers (IEEE)802.11 and the industry developed wireless Bluetooth standard.

The most common antenna used in a mobile subscriber unit is a monopole.A monopole antenna most often consists of a single wire or otherelongated metallic element. A signal transmitted from such a monopoleantenna is generally omnidirectional in nature. That is, the signal issent with approximately the same signal power in all directions in agenerally horizontal plane. Reception of a signal with a monopoleantenna element is likewise omnidirectional. A monopole antennatherefore cannot differentiate between signals originating from onedirection versus a different signal originating from another direction.Although most monopole antennas do not produce significant radiation inthe elevation plane, the expected antenna pattern in three dimensions istypically a donut-like toroidal shape, with the antenna element locatedat the center of the donut hole.

Unfortunately, CDMA communication systems are typically interferencelimited. That is, as more and more subscriber units become active withina particular area and share access to the same base station,interference increases among them, and thus so does the bit error ratethey experience. To maintain system integrity in the face of increasingerror rates, often the maximum data rate available to one or more usersmust be decreased, or the number of active units must be limited inorder to clear the radio spectrum.

It is possible to eliminate excessive interference by using directiveantenna at either the base station and/or the mobile units. Typically, adirective antenna beam pattern is achieved through the use of a phasedarray antenna at the base station. The phased array is electronicallyscanned or steered desired direction by controlling the phase angle of asignal input to each antenna element.

However, phased array antennas suffer decreased efficiency and gain aselements become electrically small as compared to the wavelength of theradiated signals. When phased arrays are used or attempted to be used inconjunction with a hand-held portable subscriber unit, the antenna arrayspacing must be relatively small and therefore antenna performance iscorrespondingly compromised.

SUMMARY OF THE INVENTION

Several considerations should be taken into account when designing anantenna for a hand-held wireless device. For example, carefulconsideration should be given to the electrical characteristics of theantenna so that propagating signals satisfy predetermined standardsrequirements such as, for example, bit error rate, signal to noise ratioor signal to noise plus interference ratio.

The antenna should also exhibit certain mechanical characteristics tosatisfy the needs of a typical user. For example, the physical length ofeach element of the antenna array depends upon the transmit and receivesignal frequency. If the antenna is configured as monopole, the lengthis typically a quarter length of a signal frequency; for operation at800 MegaHertz (MHZ) (one of the more popular wireless frequency bands) aquarter wavelength monopole must typically be in the range 3.7″ long.

The antenna should furthermore present an esthetically pleasingappearance. Especially when used in a mobile or handheld portable unit,the whole device must remain relatively small and light with a shapethat allows it to be easily carried. The antenna therefore must bemechanically simple and reliable.

In CDMA systems in particular, another consideration involvescontrolling the capacity of the overall network. Some have provided foradaptive antenna arrays for use on a reverse link of a CDMA system in ahandset. These directional antenna arrays can be used to increase systemperformance by decreasing interference from surrounding base-stationsand/or other handsets. However, employing directional antennas on thereverse link complicates the performance of power control systems. Thatis, as in most wireless communication systems, the power level ofsignals radiated from handsets must be carefully controlled in order toavoid interference to other handsets so that the signal powers arrive atthe base or other central site within a known power level range.

The present invention comes about from realizing the advantages of amobile-subscriber device that uses a directional or other adaptiveantenna array together with a separate transmit antenna. The directionaladaptive antenna array, which is used only to receive signals, maytypically consist of a number, N, of monopole antenna elements. Thesemonopole elements can be formed as conductive segments on a portion of adielectric substrate such as a printed circuit board. To complete thearray, at least one element is designated as an active antenna elementwhich is also disposed on the same substrate as one or more passiveelements. In a preferred embodiment, the active element is disposed inthe center of the array and the number of passive elements is two.

The separate transmit antenna may be integrated with the receive array.In a preferred embodiment, the transmit antenna is an omnidirectionalelement.

In other embodiments, the transmit antenna may be physically separatedsuch as on the opposite side of the housing. That is, the receiver arraymay be positioned on the top of the handset with the transmit antenna onthe lower portion thereof. In either case there is a separate receiveand transmit interface port to the two antennas.

By utilizing a horizontally polarized transmit and vertically polarizedreceive array, isolation between the two antennae is improved.

CDMA based systems that exist today, such as IS-95 and IS-2000, have acapacity limitation problem. The limitations largely occur on theforward link, and result from some channel interference. Thisinterference originates from both adjacent cells as well as from userswithin the same cell. Indeed, the difference in capacity between theforward and reverse links can be estimated to be as high as 50 to 100%.For voice and circuit switched data systems, the number of users thatcan be simultaneously supported is defined by the less capacious of thetwo links. Therefore, the limitation on the forward link actually limitsthe total number of users, and the excess capacity of the reverse linkis wasted.

The use of an adaptive antenna in the subscriber unit on the receiveside has the potential to increase the forward capacity to levels equalto or greater than the reverse capacity. This allows for a significantincrease in the overall number of users without directly increasing thereverse capacity.

It is also envisioned that other types of systems, such as Time DivisionDuplex (TDD) systems, may also advantageously use the adaptive array forreceive but to steer in an omnidirectional mode during transmit periods.The effect is achieves a similar result. It is also expected that whenTDD systems are in a stationary or slow moving environment, adirectional transmit may also be able to be utilized.

In accordance with its key aspects, the present invention consists of anantenna system in which an adaptive array is used for receiving signalsand an omnidirectional antenna is used for transmitting. In preferredembodiments, the adaptive antenna is integrated into the housing of ahandheld wireless communication unit, such as a mobile telephone unit,personal digital assistant or the like.

The adaptive array used for receive mode is preferably an array thatuses parasitic, passive elements to achieve directionality.

In further aspects, the omnidirectional transmit antenna is physicallyand/or electrically separated from the receiver array. Theomnidirectional transmit antenna may be integrated at a differentpolarity. For example, a vertically polarized receive array may have ahorizontally polarized transmit element. In other instances, theseparation can be provided by a physical distance such as by integratingthe transmit antenna and the base of a handheld telephone unit.

The exact type of Radio Frequency (RF) modulation associated with theinvention may be of many different types. For example, the invention canbe utilized in Code Division Multiple Access (CDMA) systems as well asother Orthogonal Frequency Division Multiplexing (OFDM) or spreadspectrum systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a high level schematic diagram of a wireless communicationdevice incorporating an adaptive antenna array.

FIGS. 2A–2C show various arrangements in which a horizontally polarized,or predominantly horizontally polarized, omnidirectional transmitantenna is incorporated within the same device.

FIGS. 3A–3C illustrate an alternate embodiment for the transmit antenna,mounted on the backside of a handset.

FIG. 4 is a more detailed plan of a three element receive array.

FIG. 5 is a circuit diagram showing one possible feed structure for thearray.

FIG. 6 is a schematic diagram illustrating how the array can beintegrated into a handset.

FIGS. 7A–7C illustrate a three-dimensional radiation pattern, azimuthalpattern and elevational pattern for the adaptive array.

FIGS. 8A–8C illustrate the gain patterns of a horizontal monopoletransmit element in the three-dimensional, azimuthal and elevationalplanes.

FIGS. 9A–9C illustrate gain patterns of the bent horizontal monopoleelement operating in a PCS radio frequency band.

FIGS. 10A–10C illustrate three-dimensional, azimuthal, and elevationalpatterns for a bent monopole transmit element and its affect on thereceive array.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

Turning attention now to the drawings, FIG. 1 illustrates a wirelessdevice 100 that consists of a housing 110 having incorporated therein anantenna array 120. In general the device 100 is some form of wirelesscommunications device, such as a cellular mobile handset, or a personaldigital assistant such as a Palm Pilot.

The antenna array 100 provides for directional reception of forward linkradio signals. The forward link signals may be transmitted from a basestation, in the case of a cellular handset 100, or from a access point,in the case of a wireless data unit 100 making use of wireless localarea network (WLAN) protocols. By directively receiving signalsoriginating more or less from the location of a particular base stationand/or access point, the antenna array 120 assists in reducing theoverall effect of intercell interference and multipath fading for themobile unit 100. Moreover, as will be understood shortly, since antennabeam patterns generated by the antenna array extend outward in a desireddirection, but are attenuated in most other directions, less power isrequired for effective transmission by the base station.

In an example embodiment, the antenna array 120 consists of a centerelement 102 and a pair of passive elements 104, one on each sidethereof. As will be understood shortly, the passive elements 104 caneach be operated in either a reflective or directive mode; it is throughthis expediency that the array 120 can be steered to a particulardirection. Although this embodiment shows three elements, it should beunderstood that the array 120 is not so limited, and that one, four, oreven more passive elements may be included. Yet other embodiments arepossible for the antenna array such as phased array, where the centerelement 102 is absent and the other elements are themselves used asactive elements, together with active signal combining circuitry. Webelieve that a simple N passive element array is preferred, however,because of its low cost and high radiation efficiency.

FIGS. 2A–2C illustrate various possible placements for a separatetransmit antenna 200 in accordance with the present invention. In theembodiment shown in FIG. 2A, the transmit antenna 200 is placed on thesame circuit board as the antenna array 120. In this particularembodiment, the transmit antenna 200 has a horizontal orientation asopposed to the vertically oriented elements of the receiver array 120.This orthogonal arrangement provides for greater isolation between thetwo antenna sets.

In an alternate embodiment shown in FIG. 2B, the transmit antenna 200can be placed at the lower end of the handset 110 housing. This providesfor even more electromagnetic isolation due to the physical distancebetween the horizontal element 200 and the elements of the receive array120. This also tends to move a high power microwave region associatedwith the transmit antenna 200 closer to a region of the user's chin,rather than the user's brain.

In still other embodiments, as shown in FIG. 2C, an end portion of thetransmit antenna 200 may be bent. The bent portion, which itself maythen become more or less parallel with the elements of the directionalarray, allows for more design freedom. For example, this type of antennacan be used at a lower frequency where the overall length of the antennamust be longer but must still fit within the width of the handset. Thebent element 200 might also be used to accommodate other componentswithin the handset 110 such as a keypad. The bent arrangement alsoavoids radiation in the horizontal plane when the handset is held near avertical position. This can provide for improved performance in allorientations of the handset 110.

FIGS. 3A–3C show still further possible embodiments of the transmitelement 200, with FIG. 3A being a side view and FIG. 3B being a rearview of the housing 110. Here the transmit antenna 200 is a relativelyshort length for operation at relatively high frequencies such as inPersonal Communication Services (PCS) type frequencies that typicallyare in the range of 1900 MegaHertz (MHZ). However the element 200 can beprovided with a hinge 210 allowing for an elongated section 220 toprovide dual mode operation. The overall length of the fully deployedantenna element can be made to resonate at a lower frequency, such asthe 800 (MHZ) frequency associated with standard cellular telephonecommunication. The hinged or flipping arrangement for the element 200assures that it can either resonate within one band or the other. It istherefore preferred to sliding or telescoping arrangements which mightlead to the user not fully deploying the element 200 at the properlength.

In this embodiment a feedpoint 230 associated with the transmit antenna200 may actually be placed in an offset position that is not completelyat one end of the element 200. This offset feedpoint location 230 allowsthe resonant length ratio to fit the 1900/800 MHZ frequency ratio.

FIG. 4 is more detailed view of the adaptive directional array 110. Herethe array 110 is disposed on portions of a dielectric substrate such asa printed circuit board, including the center element 102 and passiveelements 104A and 104C previously described. Each of the passiveelements 104 can be operated in a reflective or directive mode as willbe understood shortly.

The center element 102 comprises a conductive radiator 106 disposed onthe dielectric substrate 108. The passive elements 104A and 104Cthemselves each have an upper conductive segment 110A and 110C as wellas a corresponding lower conductive segment 112A and 112C. Thesesegments 110A, 110C, 112A, and 112C are also disposed on the dielectricsubstrate 108. The lower conductive segments 112A and 112C are ingeneral grounded. Also, in general, the upper segments 110A and 110C andthe lower 112A and 112C are of equal length.

When the upper conductive segment of one of the passive elements 104,for example the upper conductive segment 110A, is connected to therespective lower conductive segment 112A, the passive element 104Aoperates in a reflective mode. This results in received Radio Frequency(RF) energy being reflected back from the passive element 104A towardsits source.

When the upper conductive segment 110A is open (i.e., not connected tothe lower conductive segment 112A or other ground potential) the passiveelement 104A operates in a directive mode, in which the passive element104A essentially is invisible to the propagating RF energy which passestherethrough.

In one embodiment, the center element 102 and the passive elements 104Aand 104D are fabricated from a single dielectric substrate such aprinted circuit board with the respective elements disposed thereon. Thepassive elements 104A and 104C can also be disposed on a deformable orflexible substrate or attached to one surface of the center element 102as well.

A microelectronics module 122, including respective switch modules 116Aand 116C, may also be disposed on the same substrate 108 with conductivetraces 124 being provided therebetween. The signals carried on theconductive traces 124 control the state of the components within themicroelectronic modules 116A and 116C that achieve particular operatingstates for the passive elements 104A and 104C, e.g., to place them ineither the reflective or directive state as described above. Furtherconnected to the microelectronics module 122 is an interface 125 forproviding electrical signal control connectivity between the array 120and an external controller device such as located in the remainder ofthe handset 100. Interface 125 can be constructed from either a rigid orflexible material such as ribbon cable or other connector, for example.

FIG. 5 illustrates one possible feed structure for the array 120 in moredetail. A switch control and driver 142 associated with the electronicsmodule 122 provides logic control signals to each of the respectivecontrol modules 116A and 116C associated with the respective elements104A and 104C. For example, each such control module 116 may haveassociated with it a switch S1 or S2 and two impedances Z1 and Z2. Thestate of the switches S1 or S2 provides for connection states of eitherconnecting the first impedance Z1 or the second impedance Z2. In apreferred embodiment, the second impedance Z2 may be 0 ohms and thefirst impedance Z1 may be infinite, thus providing the desired shortcircuit to ground or open circuit. However, it should be understood thatother values of the impedances Z1 and Z2 are possible, such as variousreactive values.

Here it is also evident that the center element 102 is being directlydriven to the receiver circuitry 300 associated with the handset. Thus,unlike other types of directive arrays, this particular directive array120 has an advantage in that it is quite simple in operation, andcomplex combiners and the like are not necessary.

FIG. 6 is a exploded view of one possible implementation showing thedirective array 120 formed on a printed circuit board and placed withina rear cover of a handset, for example. A center module 410 may includeelectronic circuitry, radio reception and transmission equipment, andthe like. A final module 420 may serve as, for example, a front cover ofthe device. What is important to see here is that the printed circuitboard implementation of the 100 can be easily fit within a handset formfactor.

FIGS. 7A and 7B are antenna patterns illustrating performance of thearray 120 as housed in a handset. The gain achievable is about 3 dBi.FIG. 7A is a three dimensional radiation pattern (in the X, Y and Zdirections with respect to the referenced diagram shown for the handset500).

FIG. 7B illustrates the azimuthal radiation pattern achievable when oneof the elements is placed in directive mode and the other element isplaced in reflective mode. The conducting element (which is madeelectrically longer in the Z direction), intercepts the received radiowave and reflects it. This creates a null in the negative X direction.Since there is no electromagnetic blockage in the +X direction, the wavepasses through and creates a peak. The dimension of the circuit board inthe X direction is not similar to the resonant wavelength, so that thesignal is able to circulate all the way around the azimuthal plane.

The pattern in FIG. 7C, an elevational pattern, should be compared to anideal symmetrical pattern to illustrate the effect of the housing 110.The comparison shows that the overall effect on the azimuthal plane is aslight skewing of the beam, about 15° away from the X-axis. The patternof FIG. 7C also illustrates “necking-down”, which is an effect ofplacing the radiating element in a handset. Good directivity is seen, atleast along an approximate 180° azimuthal plane, although skewing isevident.

FIGS. 8A–8C are similar to FIGS. 7A–7C, although illustrate patterns thehorizontal transmit antenna element 200. This particular embodiment,with the reference physical drawing 510 shown in the upper left handcorner, was for a bent horizontal monopole element. The gain pattern inthree-dimensions is relatively uniform, as shown in FIG. 8C. Theradiation pattern approaches a symmetric toroid with a gain ofapproximately 2.1 dBi. Again, the radiation pattern is offset somewhatthrough the effects of the handset enclosure 110. However, relativelyomnidirectional performances, other than in the azimuthal plane (asshown in FIG. 8B) is the overall desired effect.

FIGS. 9A–9C are simulated gain patterns of a bent horizontal monopoledesigned for the 800 MHZ cellular band, but operating in the higherfrequency PCS band. The radiation pattern, as is evident from the viewof FIG. 9A, is a cut toroid standing its “uncut” side. The gain is 4.2dBi. The antenna is evidently radiating at its higher order mode, but isradiating effectively and thus can be used as a PCS radiator at 1900MHZ. As evident from FIGS. 9B and 9C, as at least some useable radiationpattern is seen in the azimuthal direction.

Finally, FIGS. 10A–10C illustrate the effect of adding a bent monopoletogether with the array 120 through a simulation process. In thissimulation, a horizontal bent monopole 200 and the extending groundstrip were added to the antenna array 120; only slight distortions werefound. The beam is tilted upward by 15° (as shown in the elevationalplot of FIG. 10C). The gain provided is 4.7 dBi with a beamwidth of 145°in the azimuthal plane. This illustrates that the bent monopole does notappreciably affect the operation of the array in the directional modes.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A system for reducing the overall effect of intercell interferenceand multipath fading of mobile communication device, comprising: a basestation for transmitting signals to a mobile communication device andreceiving signals from the mobile communication device; an adaptivedirectional receive antenna array coupled to the mobile communicationdevice for receiving the transmitted signals from the base station; andan omnidirectional transmit antenna coupled to the mobile communicationdevice for transmitting signals to the base station.
 2. A system as inclaim 1, wherein the adaptive receive array comprises at least oneparasitic element.
 3. A system as in claim 1, wherein the transmitantenna comprises a radiating element disposed at a differentpolarization with respect to at least one of a plurality of elements ofthe receive array.
 4. A system as in claim 3, wherein the receive arrayis vertically polarized and the transmit antenna is horizontallypolarized.
 5. A system as in claim 3, wherein the transmit antennapolarization is orthogonal to receive array polarization.
 6. A system asin claim 1, wherein the omnidirectional transmit antenna is physicallyseparated from the receive array.
 7. A system as in claim 1, wherein themobile communication device is used with Time-Division Duplex system,whereby the array is used during transmit time periods be forced tooperate in a directive mode during at least some of a receive timeperiod.
 8. A system as in claim 1, wherein the device uses a CodeDivision Multiple Access modulation.
 9. A system as in claim 1, whereinan Orthogonal Frequency Division Multiplex modulation is used.
 10. Asystem as in claim 1, wherein the omnidirectional transmit antenna andthe adaptive receive antenna array are integrated on a single dielectricsubstrate.
 11. A system as in claim 1, wherein the omnidirectionaltransmit antenna is located at a base of a housing of a hand portabledevice and the receive array is located in a top portion of the housing.12. A system as in claim 1, wherein the omnidirectional transmit antennaand the receive array are both located in a top portion of a housing ofa handheld portable device.
 13. A system as in claim 1, wherein theomnidirectional transmit antenna is bent.
 14. A system as in claim 1,wherein the omnidirectional transmit antenna is attached to a rearportion of a housing.
 15. A system as in claim 14, wherein theomnidirectional transmit antenna includes a hinge for extending andretracting a length of the transmit antenna.
 16. A system as in claim 1,wherein the adaptive directional receive antenna array comprises anactive antenna element and at least one passive antenna element.
 17. Asystem as in claim 16, further comprising a switch for coupling the atleast one passive antenna element to one or more impedances in order toaffect the directivity of the adaptive directional receive antennaarray.
 18. A system as in claim 1, wherein a portion of the adaptivedirectional receive antenna array extends through a housing of a handportable device.
 19. A system as in claim 1, wherein the adaptivedirectional receive antenna array and the transmit antenna beingintegrated into a housing of a hand portable device.